Method for imparting smoke color and flavor to food

ABSTRACT

A tar-depleted, concentrated liquid smoke is made that has superior flavoring and coloring abilities, low phenolic content, and a low acid content. It may also be partially neutralized to form a low viscosity, partially neutralized, tar-depleted, concentrated, liquid smoke composition. Both the partially neutralized and unneutralized compositions are suitable for use in commercial process equipment to make smoke impregnated cellulosic food casings and to impart smoke color, odor and flavor to foodstuff encased therein.

This application is a division of prior U.S. application Ser. No.465,924 filed Feb. 14, 1983, now U.S. Pat. No. 4,540,613.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to: (a) a method for preparing a concentrated,liquid smoke from a tar-depleted, liquid smoke solution, (b)tar-depleted, concentrated liquid smoke compositions, (c) food casingscolored and flavored with tar-depleted, concentrated, liquid smokecompositions, (d) a method for preparing a smoke colored and flavoredfoodstuff encased in a casing, (e) a method for neutralizing atar-depleted, concentrated liquid smoke, and (f) tar-depleted,concentrated, partially neutralized liquid smoke compositions.

2. Description of the Invention

Tubular cellulosic food casings are used extensively for processing agreat variety of meat products and other food items. The food casingsare generally thin-walled tubing of various diameters prepared fromreconstituted materials, such as regenerated cellulose. Cellulosic foodcasing may also be prepared with fibrous webs embedded in the wallthereof, such casings commonly being referred to as "fibrous foodcasings."

The many different recipes and modes of processing that are used by theprocessed food industry to suit different tastes, and even regionalpreferences, generally necessitate the use of food casings with avariety of characteristics. In some instance, for example, food casingsare required to have multifunctional uses wherein they serve ascontainers during the processing of a food product encased therein, andthen also serve as a protective wrapping for the finished product. Inthe processed meat industry, however, the food casings used in thepreparation of many types of meat products, such as various types ofsausages, such as frankfurters, bolognas and the like, beef rolls, hamsand the like, are frequently removed from about the processed meatproduct prior to slicing and/or final packaging.

Surface appearance and flavor are important factors in the commercialand consumer acceptance of processed meat products, and a common featureof most varieties of such products involves the use of "smoking" forimparting characteristic flavor and color thereto. The "smoking" of foodproducts is generally accomplished by the food processor subjecting thefood product to actual contact with smoke in a gaseous or cloud-likeform. Such "smoking" processes, however, have not been consideredcompletely satisfactory for a variety of reasons, including theinefficiencies and lack of uniformity of the "smoking" operation.Because of the shortcomings experienced, many meat packers now employvarious types of liquid aqueous solutions of wood-derived smokeconstituents, commonly called "liquid smoke solutions" that have beendeveloped and used commercially in the food processing industry for theprocessing of many types of meat and other food products. Forconvenience in this specification, these commercially available "liquidsmoke" solutions in their as-purchased state will be frequently referredto herein as "as-is" liquid smoke.

The application of "liquid smoke solutions" to meat products isgenerally carried out in a variety of ways, including spraying ordipping an encased food product during the processing thereof, or byincorporating the "liquid smoke solution" in the recipe itself. Theactual operation of "smoking" by spraying or dipping is not completelysatisfactory due to inability to treat the encased product uniformly,and incorporation of "liquid smoke solution" in the meat recipe does notalways provide the desired surface appearance because of dilution ofsmoke ingredients. Incorporation in the recipe also reduces thestability of the meat emulsion, and will adversely affect taste if highconcentrations are used. Application of liquid smoke to encased foodproducts by the food processor, such as by spraying or dipping, alsocauses unwanted pollution and equipment corrosion problems for the foodprocessor. In addition, encased sausages treated by application of theliquid smoke during commercial processing have been found to yield,after peeling the casing from the treated encased food product, sausageswhich are lacking in smoke color uniformity from sausage to sausage, andfrom batch of sausages to batch of sausages. What is even moreundesirable is the lack of uniformity of coloration which often appearson the surface of the individual sausages, including light and darkstreaks, light and dark blotches, and even uncolored spots whichespecially appear at the ends of sausages.

Several methods are known for coating either the interior or theexterior of a food casing with various liquid substances designed tomeet particular processing requirements, as, for example, substancesthat affect the adhesion properties of the casing. Some of the coatingsknown in the art contain a liquid smoke as a constituent thereof.However, none of these coatings applied to sausage casings have beenknown to impart smoke color and flavor to the food product to a suitableextent.

Known methods for coating as "as-is" type of liquid smoke solutioninternally in a casing have been found to be costly and also have beenfound to limit the speed of a continuous high speed production line.

Known methods for coating the external surface of a casing, particularlya cellulosic gel-stock casing, with "as-is" type liquid smokes, resultin problems due to the tar content of these smoke solutions. That is,during the coating process, tarry deposits accumulate on the carrierrolls and the squeeze rolls of the treatment unit, which eventuallyforces shutdown of the treatment system.

One solution to the above-mentioned problems of imparting smoke colorand flavor to a foodstuff is to use "tar-depleted" liquid smokesolutions to coat the interior or, preferably, the exterior surface ofthe casing. However, until recently, tar-depleted liquid smoke solutionswere unavailable, and methods for making the same were unknown. Asindicated above, it has been found that when a cellulosic food casing,made from a fibrous or non-fibrous gel stock, is treated with a highlyacidic (pH of about 2.0 to 2.5) tar-containing, aqueous liquid smoke,tarry deposits accumulate on the carrier rolls and the squeeze rolls ofthe smoke treatment unit, causing the casing to stick to the rolls andeventually forcing shutdown of the unit. The acidity of the liquid smokealso may interfere with peelability of the casing by interfering withthe action of the peeling aid used, such as, for example, carboxymethylcellulose. Aqueous liquid smokes are generally very acidic, having a pHof 2.5 or less and a titratable activity of at least 3 weight percent.

It was found that tar could be removed from the liquid smoke byneutralizing the as-is liquid smoke to precipitate the tar, and that useof this neutralized, tar-depleted liquid smoke to treat a gel stockcasing would eliminate the tarry deposit accumulation problem. This isdisclosed in copending U.S. patent application Ser. No. 417,172, filed14 Sept. 1982 by Nicholson, now U.S. Pat. No. 4,431,032.

Contrary to the previous belief in the art, the tar-depleted liquidsmoke still possesses significant smoke coloring and flavoringcapability. It has been generally believed that the tars in a liquidsmoke mainly contribute to the coloring and flavoring ability of theliquid smoke. However, it has been found that this is not the case, andthat other constituents of the liquid smoke, believed to be mainly theacids, the phenols and the carbonyls, have a more significant role inthe coloring and flavoring ability of the liquid smoke.

One problem with the neutralizing method for forming a tar-depletedliquid smoke is that, although the liquid smoke compositions madethereby have significant coloration ability or "staining power", thecoloration ability declines with increasing pH or neutralization. Thislimits its applicability in applications wherein a high colorationability is desired.

Another method, using a "solvent extraction" process, may be employed tomake tar-depleted liquid smoke. Such a process is disclosed in copendingU.S. patent application Ser. No. 417,173, filed 14 Sept. 1982 byNicholson, now U.S. Pat. No. 4,431,033. For example, such a processcomprises contacting a tar-containing aqueous smoke solution having anabsorptive power of at least about 0.25 at a wave length of about 340nm, with either a nonreactive or reactive organic liquid solvent whichhas a hydrogen bonding solubility parameter of at least about 2.7 andwhich is immiscible in the aqueous liquid smoke solution underconditions sufficient to form a tar-enriched solvent fraction and atar-depleted liquid smoke fraction, and separating the liquid smokefraction to form a tar-depleted liquid smoke. Using such a solventextraction method, it becomes possible to make tar-depleted liquidsmokes having a high capability to impart smoke color, odor, and flavor,without requiring neutralization of the tar-containing liquid smoke.

The tar-depleted liquid smoke made from the solvent extraction process,unless it is neutralized, is generally highly acidic, which may alsointerfere with action of the peelability agents, such as certain watersoluble cellulose ethers, which may be used on the casing. To alleviatethis problem, the tar-depleted liquid smoke may be partiallyneutralized. However, since the coloration ability of the liquid smokedeclines with increasing pH, the tar-depleted liquid smoke is only"partially neutralized" to a degree such that the peelability agent isnot significantly affected and the coloration ability of the smoke isretained. The term "partially neutralized", as used herein, is intendedto refer to liquid smoke compositions having a pH greater than about 3,preferably having a pH within the range of from about 3 to about 6.5,and even more preferably having a pH within the range of from about 3 toabout 5. By providing a partially neutralized, tar-depleted liquid smokemade from a solvent extraction process, the problems due to acidity areavoided while retaining a significant degree of the coloring ability ofthe original as-is liquid smoke.

Unconcentrated liquid smoke compositions, whether partially neutralizedor unneutralized, have been found particularly suitable for use withfibrous cellulosic food casings. When used with nonfibrous casings, ithas been found that unconcentrated liquid smokes impart a smoke color,odor and flavor to the foodstuff, but not in a quantity to besufficiently acceptable for all commercial applications. Becausenonfibrous casings are thinner than fibrous casings, sufficientunconcentrated liquid smoke cannot be "coated" on, applied to, orincorporated in the wall of the casing to an extent sufficient to alwaysimpart the desired smoke color, odor and flavor to a foodstuff.

SUMMARY OF THE INVENTION

The present invention includes a method for concentrating tar-depletedliquid smoke solutions which comprises providing an unneutralized,tar-depleted liquid smoke composition made from a solvent extractionprocess, and concentrating the unneutralized tar-depleted liquid smokeas described below. The concentrated liquid smoke product has surprisingand advantageous physical properties. It may be optionally neutralizedto provide a tar-depleted, concentrated, partially neutralized, liquidsmoke composition. As practiced in the prior art, when an as-is liquidsmoke is concentrated, there is an increased concentration ofundesirable chemical substances, for example, tars. Certain otherconstituents which are desirable, such as phenols, which contribute tothe flavoring and coloring ability, may also become concentrated to anextent sufficient to cause an undesirably "strong" flavor. It has alsobeen found that when a neutralized liquid smoke is concentrated, thereis a significant and undesirable increase in viscosity, renderingthereby the resulting concentrated liquid smoke unsuitable forcommercial use. It has, therefore, been impractical to use suchconcentrated smokes because of the increased tarring problem and theundesirably high viscosity that occurs when the smoke is used in aneutralized state.

By the practice of this invention, it is possible to make a concentratedliquid smoke solution that has substantially increased staining power, alow viscosity when the liquid smoke is neutralized, and a low phenoliccontent.

It has been found that the increase in viscosity of neutralized liquidsmoke solutions resulting from the concentration thereof is in largepart due to the salts of neutralization that are formed when the acids,mostly acetic acid, in the liquid smoke react with the neutralizationagent. The concentration of these salts of neutralization increasesproportionally with the degree of concentration, resulting ultimately inan excessive concentration of these salts and, thus, an undesirably highviscosity.

Suprisingly, it has been found that when concentrating an unneutralized,tar-depleted, liquid smoke, the acid-content is not proportionallyincreased, but the amount of acid in the liquid smoke decreases with thedegree of concentration of the liquid smoke. That is, as theunneutralized, tar-depleted smoke is concentrated, the acids causing theviscosity difficulties are apparently volatilized to a significantdegree. Thus, it is possible to make concentrated liquid smokes, whileretaining a suitably low viscosity. The concentrated, liquid smokecompositions of the invention, in addition to having a low total acidcontent and a low viscosity when neutralized, are tar-depleted, and havethe processing advantages found with unconcentrated tar-depleted liquidsmokes. They also have substantially increased smoke coloring andflavoring capabilities over non-concentrated tar-depleted liquid smokes.

The higher viscosity of concentrated as-is smokes of the prior art isalso due in part to the presence of the high molecular weight polymerictar constituents in the liquid smoke composition. The low amount of tarsin the tar-depleted compositions of this invention contribute to the lowviscosity of both the unneutralized and partially neutralized forms.

Thus, an aspect of the present invention is a method for making atar-depleted, concentrated liquid smoke which comprises (1) contactingan aqueous, tar-containing, unneutralized liquid smoke solution and aliquid solvent at a volume ratio between about 1:1 and about 65:1,respectively, under conditions sufficient to form a tar-enriched, liquidsolvent fraction and an aqueous, tar-depleted, liquid smoke fraction,the tar-depleted, liquid smoke fraction having an absorptive power of atleast about 0.15, preferably at least about 0.25, at a wave length of340 nm, and having a light transmittance of at least about 50%,preferably about 65%, the tar-containing liquid smoke solution having anabsorptive power of at least about 0.25 at a wave length of 340 nm, theliquid solvent being nonreactive with the liquid smoke solution orreactive with the liquid smoke solution to form a derivative liquidsolvent, the liquid solvent being immiscible in the liquid smokesolution, the liquid solvent having a hydrogen bonding solubilityparameter in the environment of the liquid smoke solution of at leastabout 2.7; ( 2) separating the tar-depleted, unneutralized liquid smokefraction from the tar-enriched liquid solvent fraction; and (3)concentrating the tar-depleted, unneutralized liquid smoke fraction at atemperature less than about 70° C., preferably less than about 50° C.,to a concentration ratio of between about 2:1 and about 5:1, preferablybetween about 3:1 and about 4:1, to form a tar-depleted, concentrated,liquid smoke composition having a total acid content less than about 40weight percent, preferably less than about 35 weight percent.

In a preferred embodiment, the present invention comprises atar-depleted liquid smoke composition having a total acid contentgreater than about 12 and less than about 40 weight percent, preferablyless than about 35 weight percent, an absorptive power of at least about0.15, preferably at least about 0.25, at a wave length of 340 nm, aviscosity of less than about 500 centipoise at 25° C., a carbonylcontent greater than about 200 mg/ml, and a phenol content less thanabout 5% of the carbonyl content. Additionally, this liquid smokecomposition has a pH of between about 3 and about 6.5.

In a further preferred embodiment, the present invention comprises afood casing having an absorptive index of at least 0.25 at a wave lengthof 340 nm and containing a tar-depleted liquid smoke composition havingan absorptive power of at least about 0.15 at a wave length of 340 nm, atotal acid content greater than about 12 and less than about 40 weightpercent, a carbonyl content greater than about 200 mg/ml, and a phenolcontent less than 5% of the carbonyl content. Preferably, the casing hasan absorptive index of from about 0.3 to about 0.9.

Additionally, the present invention comprehends methods of manufacturingthe preferred tar-depleted liquid smoke composition and the preferredfood casing which have been defined in the foregoing two paragraphs.

The present invention also includes tar-depleted, concentrated, liquidsmoke compositions having a total acid content less than about 40 weightpercent, preferably less than about 35 weight percent, an absorptivepower of at least about 0.15, preferably at least about 0.25, at a wavelength of 340 nm, and a viscosity of less than about 500 centipoise at25° C.

The present invention also includes a method for making a tar-depleted,concentrated, partially neutralized liquid smoke composition whichcomprises (1) contacting an aqueous, tar-containing, liquid smokesolution and a liquid solvent at a volume ratio of from between about1:1 and about 65:1, respectively, under conditions sufficient to form atar-enriched, liquid solvent fraction and an aqueous, tar-depleted,liquid smoke fraction, the tar-depleted, liquid smoke fraction having anabsorptive power of at least about 0.15, preferably at least about 0.25,at a wave length of 340 nm, and having a light transmittance of at leastabout 50%, preferably at least about 65%, the tar-containing liquidsmoke solution having an absorptive power of at least about 0.25 at awave length of 340 nm, the liquid solvent being nonreactive with theliquid smoke solution or reactive with the liquid smoke solution to forma derivative liquid solvent, the liquid solvent being immiscible in theliquid smoke solution, the liquid solvent having a hydrogen bondingsolubility parameter in the environment of the liquid smoke solution ofat least about 2.7; (2) separating the tar-depleted, liquid smokefraction from the tar-enriched liquid solvent fraction; (3)concentrating the tar-depleted, liquid smoke fraction at a temperatureless than about 70° C., preferably less than about 50° C., to aconcentration ratio of between about 2:1 to about ;B 5:1, preferablyfrom about 3:1 to about 4:1, to form the tar-depleted, concentrated,liquid smoke composition; and (4) neutralizing the tar-depleted,concentrated, liquid smoke composition to a pH greater than 3,preferably between about 3 and about 6.5, more preferably between about3 and about 5, to form a tar-depleted, concentrated, partiallyneutralized liquid smoke composition, the tar-depleted, concentrated,partially neutralized, liquid smoke composition having a viscosity lessthan about 500 cp, preferably less than about 250 cp, at 25° C.

The present invention also includes a tar-depleted, concentrated,partially neutralized, liquid smoke composition having a viscosity lessthan about 500 cp, preferably less than about 200 cp, at about 25° C., apH greater than 3, preferably between about 3 and about 6.5, anabsorptive power of at least about 0.25, at a wave length of 340 nm; anda total acid content less than about 40 weight percent, preferably lessthan about 35 weight percent.

The present invention also comprises a food casing that is colored andflavored by a concentrated liquid smoke composition wherein the wall ofsaid casing contains smoke color and flavor constituents and has anabsorptive index of at least about 0.25, preferably between about 0.3and about 0.9, at a wave length of 340 nm.

The present invention also includes a method for making a food casingthat is colored and flavored by a liquid smoke composition thatcomprises treating a surface of a tubular food casing with any of theconcentrated liquid smoke compositions of this invention, eitherunneutralized or partially neutralized, in a sufficient quantity suchthat the wall of the casing contains smoke color and flavor constituentsand has an absorptive index of at least 0.25, preferably between about0.3 about 0.9, at a wave length of 340 nm.

The present invention also includes a method for imparting a smoke odor,color, and flavor to a foodstuff which comprises treating a surface of atubular food casing with any of the concentrated liquid smokecompositions of this invention, either unneutralized or partiallyneutralized, in a sufficient quantity such that the wall of the casingcontains smoke color and flavor constituents and has an absorptive indexof at least 0.25, preferably between about 0.3 and about 0.9, at a wavelength of 340 nm; stuffing the casing with foodstuff and processing thecasing with the foodstuff therein under conditions sufficient totransfer smoke color and smoke flavor constituents from the casing tothe encased foodstuff.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of apparatus suitable for treatment of theexternal surface of a food casing with the liquid smoke composition ofthis invention.

FIG. 2 is a schematic view of apparatus similar to and performing thesame functions as the apparatus of FIG. 1, but with a chamber forpartially drying the casing treated with the liquid smoke composition ofthis invention to a desired moisture content while in an inflatedcondition.

FIG. 3 is a schematic view of apparatus similar to and performing thesame function as the apparatus of FIG. 2, but with means for partiallydrying of the casing treated with the liquid smoke composition of thisinvention while in a flat condition.

FIG. 4 is an elevation view, with certain parts in cross-section, of anabsorbent-type liquid appicator-smoother assembly useful for coating thetar-depleted, concentrated liquid smoke solutions of the invention upona casing.

FIG. 5 is a graph showing the viscosity and the pH of liquid smokesolutions of the invention and also of liquid smoke solutions that wereconcentrated after they were neutralized.

DETAILED DESCRIPTION OF THE INVENTION

As used in this specification and the appended claims, the followingterms are defined as follows:

"Solution" is meant to encompass homogeneous true solutions, as well asemulsions, colloidal suspensions, and the like.

"Smoke color, odor, and flavor constituents", refers to the smoke color,odor and flavor constituents present in natural wood derived liquidsmoke solutions.

"Absorptive power" is a measure of the coloring capability of the liquidsmoke solution. Absorptive power is measured by placing 10 mg of aliquid smoke solution to be tested (either tar-containing liquid smokeor tar-depleted liquid smoke) in a disposable vial and mixing 5 ml ofmethanol therewith. The ultraviolet absorption value of the mixture isthen measured at a wavelength of 340 nm, and this value is theabsorptive power. It should be noted that whereas tar content is asignificant contributor to the absorptive power measurement, tar onlycontributes to the staining of food in a minor way, if at all. Thus, incommerically available as-is smoke solutions, absorptive power includesa measurement of the tar-content and of the coloring constituents suchas carbonyls, phenols and acids. This means that the absorptive power ofas-is smoke solutions and tar-depleted smoke solutions may be used tocomparatively rank them in smoke coloring ability. However, theabsorptive power of an as-is liquid smoke solution cannot be numericallycompared with the absorptive power of a tar-depleted smoke solutionbecause of the absorptive effect of tars.

"Absorptive index" is a measure of the coloring ability of a casingtreated with a liquid smoke solution. It is measured by cutting out 2square inches (12.9 square centimeters) of the casing to be tested andplacing the cut-out portion in 10 ml of methanol. After about 1 hour ofsoaking time, the methanol has extracted all of the smoke components outof the casing. The ultraviolet absorption value of the resulting smokecomponent-containing methanol is determined at a wave length of 340 nm,and this value is the absorptive index.

The concentrated liquid smoke compositions of the invention have a totalacid content of less than about 40 weight percent, and preferably lessthan about 35 weight percent. "Total acid content" refers to theconcentration of acids, principally acetic acid, that are present in theliquid smoke. It is reported as weight percent and since acetic acid isthe principal acid in liquid smoke, the weight percent is based onequivalents of acetic acid. These values for total acid content refer totar-depleted, concentrated, liquid smoke compositions made from as-isliquid smoke compositions having an acid content of between about 11 andabout 13 weight percent. While it is contemplated as within the scope ofthis invention that as-is liquid smoke solutions having a lower acidcontent can be used in the method of this invention, for economicalreasons as-is liquid smokes having an acid content between about 11 and13 weight percent are preferred. If an as-is smoke having a lower acidcontent is used, the expected acid content of the inventive concentratedliquid smoke composition at the same concentration ratio would beproportionally less.

Total acid content is measured by the following procedure:

1. Weigh accurately about 1 ml of liquid smoke (filtered if necessary)in a 250 ml beaker,

2. Dilute with about 100 ml of distilled water and titrate with standard0.1N NaOH to a pH of 8.15 (as measured on a pH meter),

3. Calculate the total acid content as weight percent of acetic acid(HAc), using the following conversion;

    1 ml 0.1000N NaOH=6.0 mg HAc

This method can be used to measure total acid content of tar-containingliquid smokes and tar-depleted liquid smoke solutions that have not beenneutralized.

In practice of the invention, a solvent extraction process is used toprovide a tar-depleted liquid smoke fraction. The tar-depleted, liquidsmoke fraction comprises a composition derived from an as-is aqueousliquid smoke solution and it contains smoke color, odor and flavorconstituents. It has an absorptive power of at least about 0.15 at awave length of 340 nm, and it has a light transmittance of at leastabout 50%. The tar-depleted liquid smoke fraction is prepared bycontacting the tar-containing, aqueous liquid smoke solution withsuitable nonreactive or certain reactive organic solvents, ashereinafter described, to extract the tars therefrom.

The tar-containing aqueous liquid smoke solutions useful in theinvention include commercially available as-is liquid smoke solutions.The tar-containing aqueous liquid smoke solutions should have anabsorptive power of at least about 0.25 at a wave length of 340 nm.Suitable liquid smoke solutions are generally produced by the limitedburning of wood, generally hardwood, and the absorption of the smoke sogenerated into an aqueous solution under controlled conditions. Thelimited burning keeps some of the undesirable hydrocarbon compounds oftars in an insoluble form, thereby allowing removal of theseconstituents from the final liquid smoke. Thus, by this procedure, thewood constituents previously considered desirable by the manufacturersof liquid smoke are absorbed into the solution in a balanced proportionand the undesirable constituents may be removed. Alternately, thetar-containing liquid smoke solution may be derived from the destructivedistillation of wood, that is, the breakdown or cracking of wood fibersinto various compounds which are distilled out of the wood char residue.The liquid smoke solution, resulting from either of the above processes,still contains a significant concentration of soluble tars because themanufacturers and users of liquid smoke consider the dark colored tarsto be necessary from the standpoint of imparting smoke color, odor, andflavor to foodstuffs. This type of smoke solution is representative ofthe whole spectrum of wood-derived smoke colors and flavors that areavailable. The preferred apparatus and method for manufacturing typicalliquid smoke solutions used in the invention are described in U.S. Pat.No. 3,106,473, issued Oct. 8, 1963 to Hollenbeck, and U.S. Pat. No.3,873,741 issued Mar. 25, 1975 to Melcer et al.

The light transmittance is measured for water-liquid smoke mixtures.This measured light transmittance (relative to pure water) is inverselyrelated to tar-content of the tested liquid smoke, i.e. a hightar-content results in a cloudy liquid with low light transmittance. Theprocedure for measuring light transmittance is to thoroughly mix a 1 mlaliquot of the liquid smoke with 10 ml of water, and determine itsturbidity-transmittance on a spectrophotometer using a light wavelengthof 590 nm. The higher the percent transmittance reading, the lower theresidual tar concentration in the liquid smoke composition. The desiredlight transmittance for a tar-depleted liquid smoke solution may beachieved by selection of the solvent and also by controlling the volumeratio of as-is liquid smoke solution to solvent, as shall be describedmore fully hereinafter. In general, the highest levels of lighttransmittance are achieved with the greatest quantity of solventrelative to liquid smoke.

The organic liquid solvent used in the invention should be immiscible inthe tar-containing liquid smoke solution and have a hydrogen bondingsolubility parameter in the liquid smoke environment of at least about2.7. The organic liquid solvent may be either nonreactive with thetar-containing liquid smoke or reactive with the tar-containing liquidsmoke solution to form a derivative liquid solvent. If reactive, thederivative liquid solvent should also have the same solvent propertiesas described above.

The hydrogen bonding solubility parameter, as used herein, can becalculated from known literature or experimental vapor pressure datasuch as the heat of vaporization at 25° C. The total solubilityparameter (δ_(T)) may be determined by using the relation of Equation(1). ##EQU1## where:

ΔH₂₅ =Heat of vaporization at 25° C.,

R=Gas constant,

T=Temperature, Degrees Kelvin

d=Density at 25° C., and

M=Molecular weight.

The total solubility parameter value can be separated into its hydrogenbonding (δ_(H)), polar (δ_(P)), and nonpolar (δ_(NP)) constituents. Thefollowing relationships are useful for determining the hydrogen bondingparameter value (δ_(H)). ##EQU2## where:

α=Aggregation number,

T_(b) =Boiling point in degrees absolute, and

T_(c) =Critical temperature in degrees absolute.

The theoretical basis for use of solubility characteristics is discussedin the literature. Tabulation of parameters have been published in "TheThree Dimensional Solubility Parameter and Solvent DiffusionCoefficient, "Danish Technical Press, 1967, Copenhagen, by C. M. Hansen.A list of solubility parameters can be obtained from K. L. Hoy, "Tablesof Solubility Parameters", Union Carbide Corporation, 1975, obtainablefrom Union Carbide Corporation, River Road, Bound Brook, N.J. 08805.

Suitable organic solvents include halogen di- or trisubstitutedmethanes, such as methylene dichloride, bromochloromethane, and thelike; chloroform, bromoform, and the like; acetophenone; andnon-halogenated alcohol liquids such as 2-ethylhexanol, the phenyl etherof ethylene glycol, the monohexyl ether of ethylene glycol, n-octylalcohol, n-hexyl alcohol, and n-butyl alcohol. The preferred solvent ismethylene dichloride (CH₂ Cl₂).

The tar-containing, aqueous, as-is liquid smoke and the liquid organicsolvent are contacted at a volume ratio of liquid smoke to liquidsolvent of from between about 1:1 and about 65:1, respectively, andunder extraction conditions to form a tar-enriched liquid solventfraction and a tar-depleted aqueous liquid smoke fraction. The exactratio used will depend on the particular solvent used and the lighttransmittance desired for the tar-depleted liquid smoke fraction.Generally, a lower ratio of liquid smoke to solvent is used to achieve alower tar content in the aqueous smoke product, and thereby obtain ahigher light transmittance.

The method of contacting the solvent and the liquid smoke can be anysuitable method known for solvent extraction and may include more thanone extraction stage. The contacting may occur under ambient conditionsor under elevated pressure and temperature conditions. Methods that maybe used include those using liquid-liquid cyclones, centrifugalcontactors, or countercurrent columns, including spray towers, packedcolumns, decked columns containing sieve trays or modified bubble trays,and columns with internal agitation such as rotary disc columns.

After formation of the tar-enriched solvent fraction and thetar-depleted liquid smoke fraction, the fractions are separated by anyof several methods well-known to those skilled in the art. These methodsinclude filtration, gravity decanting, liquid cycloning, and centrifugaldecanting.

The tar-depleted, liquid smoke fraction useful in the invention hassmoke coloring and flavoring ability, and has an absorptive power of atleast about 0.15 at a wave length of 340 nm, a light transmittance of atleast 50%, preferably at least 65%, and a pH of less than about 3.

The tar-depleted, liquid smoke fraction is then concentrated at atemperature of less than about 70° C., and preferably less than about50° C. It has been found that if the tar-depleted liquid smoke fractionis heated to a temperature above the indicated range, the smokeflavoring and coloring ability of the product is deleteriously affected.In addition, the tar content of the tar-depleted, liquid smoke fractionis increased to an undesirable degree when heated above the indicatedtemperatures. It is believed that this is due to temperature catalyzedpolymerization reactions of the phenols in the tar-depleted, liquidsmoke fraction.

The method of concentration may be any suitable method wherein asuitably low temperature, as explained above, is maintained. Typically,concentration is accomplished using evaporation. Examples of evaporationmethods are summarized in PERRY'S CHEMICAL ENGINEERING HANDBOOK, 4thEdition, pages 11-24 to 11-29. In order to maintain a suitabletemperature and evaporation rate it may be desirable to do theevaporation under reduced pressure. Suitable methods for evaporation arewell known and evaporators and related equipment are readily available.For concentration on a laboratory scale, the liquid smoke can beconcentrated by a forced draft of air over a large surface of the liquidsmoke. On a commercial scale, suitable methods include, but are notrestricted to, forced-circulation evaporators, long-tube verticalevaporators, preferably of the falling film type, and agitated filmevaporators. The process of the forced-circulation evaporator basicallyinvolves the forced circulation of the fluid, through pumping, past aheating element, such as heat-exchanger tubes supplied with a heatexchanger fluid. Preferably, the forced-circulation evaporator is of thesubmerged-tube type, wherein the heating element is exposed only to theliquid phase. A long-tube vertical evaporator involves the use of a longvertical heat exchanger-surface along which the liquid to be evaporatedis passed. Generally, the vaporizing surface is the inner surface ofheat-exchanger tubes, which are preferably oriented vertically andsupplied on the outer surface with a heating fluid, which is provided ata controlled temperature predetermined not to allow vaporization tooccur at the level of thermal instability of the liquid smoke. In thefalling-film type of evaporator, the liquid to be vaporized is fed tothe tops of the tubes and flows down the inner walls of the tubes as afilm, where it is heated and concentrated through evaporation. Theagitated-film or wiped-film evaporator has a heating surface comprisingthe inner surface of one relatively large diameter tube that may bestraight or tapered. Liquid is spread on the heating surface usingwipers, which maintain a close clearance to the tube wall or actuallyride on the film of liquid on the wall.

Various methods of concentrating by reduction of the water component ofthe liquid smoke solution may be employed including, but not limited tovaporization by room temperature evaporation in a low humidityenvironment. Other methods of concentration which may be employedinclude among others, "freeze drying" and "spray drying".

The tar-depleted liquid smoke of the present invention is concentratedto a concentration ratio of from about 2:1 to about 5:1, and preferablyfrom about 3:1 to about 4:1. The concentration ratio, as used herein, isthe weight of the tar-depleted liquid smoke fraction divided by theresulting weight of the unneutralized, tar-depleted, concentrated liquidsmoke. In order to obtain a tar-depleted, concentrated, partiallyneutralized liquid smoke having a low viscosity, the tar-depleted liquidsmoke fraction to be concentrated should be unneutralized. Concentratinga prior neutralized liquid smoke composition results in a concentrate ofhigh viscosity. A high viscosity is generally undesirable since itinterferes with processing methods used to apply the liquid smoke to thecasing. The finding that neutralized concentrates having a low viscositycan be formed by the method of this invention, is both unexpected andsurprising.

After the tar-depleted liquid smoke is concentrated in the abovedescribed manner, the resulting concentrate is optionally partiallyneutralized to an extent such that the pH is greater than about 3,preferably between about 3 and about 6.5, and more preferably betweenabout 3 and about 5. The temperature is controlled during the partialneutralization so that the temperature of the liquid smoke does not riseabove about 40° C., and preferably does not rise above about 30° C.

The partial neutralization of the unneutralized, tar-depleted,concentrated, liquid smoke of the invention may be accomplished bymixing either a highly alkaline solid with the tar-containing liquidsmoke, as for example CaCO₃, NaHCO₃, KOH, Ca(OH)₂, Na₂ CO₃, soda-limemixture, and NaOH pellets or flake, or by mixing the liquid smoke with ahigh pH liquid such as aqueous NaOH solution. Although, the carbonateand bicarbonate solids produce violent foaming, which may causeoperational difficulties, the neutralization reaction of the acids inthe liquid smoke with bicarbonate is endothermic, which may eliminatethe need for temperature control during the neutralization.

The rate of addition of the neutralizing material to the tar-containingliquid smoke depends on the cooling capacity of the mixing container aswell as the efficiency of the mixing means, as will be understood bythose skilled in the art. The coloring ability of the tar-depleted,concentrated, partially neutralized liquid smoke is not substantiallyaffected by temperature variations during the at least partialneutralization step, as long as the temperature of the bulk liquid ismaintained below about 40° C., and preferably below about 30° C.

The mixing container should be cooled by indirect means, as for example,brine circulating through immersed coils in a closed-circuitrefrigeration system. The reason for indirect rather than direct contactbetween the refrigerant and the liquid smoke is to avoid contaminationof the latter.

Another possible method for at least partially neutralizing thetar-depleted, concentrated liquid smoke is by contacting the latter withan ion-exchange material.

The tar-depleted, concentrated liquid smoke composition of thisinvention, whether unneutralized or neutralized, is then applied to afood casing. The food casings that are suitable for use in the inventionare tubular casings, and preferably tubular cellulosic casings, that areprepared by any one of the methods well known in the art. Such casingsare generally flexible, thin-walled seamless tubing formed ofregenerated cellulose, cellulose ethers such as hydroxyethyl cellulose,and the like, in a variety of diameters. Also suitable are tubularcellulosic casings having a fibrous reinforcing web embedded in the wallthereof, which are commonly called "fibrous food casings", as well ascellulosic casings without the fibrous reinforcement, herein referred toas "nonfibrous" cellulosic casings.

Casings conventionally known as "dry stock casings" may be used in thepractice of this invention. Such casings generally have a water contentwithin the range of from about 5 to about 14 weight percent water fornonfibrous casings, or from about 3 to about 8 weight percent water forfibrous casings, based on the total weight of the casing includingwater.

Casings conventionally known as "gel stock casings" are casings whichhave higher moisture contents than the aforementioned casings since theyhave not been previously dried. Such casings may also be used in thepractice of this invention. Gel stock casings, whether fibrous ornon-fibrous, are the type exhibiting the aforementioned tarring problemwhen treated by as-is, tar-containing liquid smoke.

The tar-depleted, concentrated liquid smoke solution of the invention,whether unneutralized or neutralized, may be applied to the outersurface of the tubular casing by passing the casing through a bath ofthe liquid smoke solution. The liquid smoke is allowed to soak into thecasing prior to doctoring off any excess liquid smoke by passing thecasing through squeeze rolls or wipers, and the like, for an amount oftime sufficient for the casing to incorporate the desired amount ofsmoke coloring and smoke flavoring constituents. The process of passingthe casing through a treatment bath, also referred to in the art as a"dip bath" or a "dip tank," may also be referred in the art as a"dipping" step. The liquid smoke of the invention may alternatively beexternally applied to the casing by methods other than dipping, such asspraying, brushing, roll-coating, and the like.

Alternatively, the tar-depleted, concentrated, liquid smoke compositionmay be applied to the internal surface of the casing by any of severalwell-known procedures such as those described in U.S. Pat. No.4,171,381, issued Oct. 16, 1979 to Chiu. These include slugging orbubble coating, spraying, and coating while shirring. The sluggingmethod for coating the inside of a casing involves filling a portion ofthe casing with the coating material, so that the slug of coatingmaterial generally resides at the bottom of a "U" shape formed by thecasing being draped over two parallel rollers, and then moving thecontinuous indefinite length of casing so that the slug of coatingmaterial remains confined within the casing, while the casing moves pastthe slug and is coated on its inside wall by the coating materialcontained within the slug.

The coated casing may be shirred by conventional methods, or prior toshirring, it may be dried and/or humidified to a water content suitablefor shirring and/or further processing. The need for conventional dryingand/or humidification after treatment with the liquid smoke compositionsof this invention depends on the water content of the casing aftertreatment and the type of casing. If the casing is a nonfibrous casing,a water content within the range of from about 8 weight percent to about18 weight percent water immediately before shirring is typical, and forfibrous casings a water content within the range of from about 11 weightpercent to about 35 weight percent water immediately before shirring istypical, where the percentages are based on the total weight of casingincluding water.

One method of treating the casing with the smoke solution of theinvention is shown in FIG. 1. In FIG. 1 a flattened, tubular, cellulosicsausage casing 10, is externally treated with the smoke composition ofthe invention during its passage over lower and upper guide rolls 13through dip tank 11 which contains the liquid smoke solution 12 of theinvention. The casing passes over lower and upper guide rolls 14 afterexiting the dip tank, and then passes between squeeze rolls 20 whichminimize any excess carry-over of the liquid smoke composition. Thetotal contact time of the casing 10 with the liquid smoke solution 12 inthe dip tank 11, and the time during which excess liquid smokecomposition adheres on the casing before it passes through the squeezerolls 20, will determine the amount of smoke coloring and smokeflavoring constituents of the tar-depleted, concentrated, liquid smokecomposition that the casing will incorporate. The total contact time ismeasured from point A to point B in FIG. 1. After the casing passesthrough squeeze rolls 20, it passes over guide roll 23 and is wound upon roll 24. The casing is then sent on to further conventionalprocessing, including conventional humidification, as may be required,and conventional shirring.

The embodiment illustrated in FIG. 2 differs from that illustrated inFIG. 1 in that in FIG. 2 the casing after passing through squeeze rolls20 is passed into a heating and drying chamber 21, wherein it is driedto the proper moisture content. The casing is inflated by a bubble ofair maintained in a relatively fixed position between squeeze rolls 20and 22 by the sealing action of rolls 20 and 22. The heating chamber 21can be any type of heating device, such as circulating hot air chambers,which will dry the sausage casing to the proper moisture content. Afterthe casing passes out of the heating chamber 21 and through squeezerolls 22, it passes over guide roll 23 and is wound up on roll 24. Thecasing is then sent on to conventional further processing, includingconventional humidification, as may be required, and conventionalshirring.

The embodiment illustrated in FIG. 3 differs from that illustrated inFIG. 2 in that in FIG. 3 the casing is dried in a flat condition whilepassing over guide rolls 25.

The preferred method for applying the tar-depleted, concentrated liquidsmoke solutions of the invention is a method wherein the exterior wallof a casing is coated by moving the casing through an inner opening of afirst flexible and resilient means, which displaces the opening edgewhile liquid is applied by rubbing contact. The liquid coating is thensmoothed by movement through the inner opening of a rotating secondflexible and resilient means. This method and an apparatus incorporatingthis method are described in U.S. Pat. No. 4,356,218, issued on Oct. 26,1982, to Chiu.

Therein the apparatus is described as an apparatus for liquid coatingthe exterior wall of an inflated flexible tubing during its longitudinalmovement comprising: (a) first flexible and resilient means with aninner circular opening having slightly smaller diameter than thediameter of the inflated flexible tubing exterior wall, the first meansbeing transversely positioned relative to the tubing axis and arrangedsuch that the inflated flexible tubing may be moved in its longitudinaldirection through said inner circular opening, so as to displace thecircular opening edge while maintaining rubbing contact therewith; (b)means for supplying said liquid to said first means (a) for distributionthereby, so as to be applied to the longitudinally moving inflatedflexible tubing exterior wall during said rubbing contact; (c) secondflexible and resilient means with an inner circular opening, the secondmeans being rotatable around the opening center and the opening havingslightly smaller diameter than the diameter of the inflated flexibletubing exterior wall, said second means being transversely positionedrelative to the tubing axis and adjacent to but spaced downstream fromthe first means (a) with respect to the longitudinally moving tubingsuch that the tubing with the coating on its external wall may be movedthrough said inner circular opening of said second means so as todisplace the rotating circular opening edge while maintaining rubbingcontact therewith for smoothing the applied liquid on the tubingexterior wall as a film of uniform thickness; and (d) means for rotatingsaid second means (c) around the tubing axis during its longitudinalmovement through said second means so as to maintain said rubbingcontact while smoothing said liquid into a continuous film ofsubstantially uniform thickness on the tubing exterior wall.

The method is described as a method for coating the exterior wall of alongitudinally moving inflated flexible tubing with liquid comprisingthe steps of (a) continuously moving the inflated flexible tubing in thelongitudinal direction along a straight line; (b) providing firstflexible and resilient means with an inner circular opening of slightlysmaller diameter than the diameter of the inflated tubing exterior wall;(c) supplying liquid to said inner circular opening of the first means;(d) moving said inflated tubing through said inner circular opening ofsaid first means and maintaining rubbing contact with the opening edgeso as to displace said opening edge and simultaneously apply said liquidto, and distribute the applied liquid around, the inflated tubingexterior wall; (e) providing second flexible and resilient means with aninner circular opening of slightly smaller diameter than the diameter ofthe inflated tubing exterior wall; (f) rotating said second means aroundits centerline axis; and (g) moving said inflated tubing with saidliquid applied on its exterior wall through the rotating second meansinner circular opening and maintaining rubbing contact with the openingedge so as to displace said opening edge while simultaneously smoothingthe liquid coating as a continuous film of substantially uniformthickness on the tubing exterior wall.

In FIG. 4 is shown an embodiment of the apparatus described inabove-cited U.S. Pat. No. 4,356,216. In FIG. 4 liquidapplicator-smoother assembly 11 is provided for coating of an inflatedflexible cellulosic tubing moving therethrough in a horizontal directionfrom left to right. The inflated flexible tubing external surface iscoated with wood-derived liquid smoke which, for example, may be pumpedto an elevated pressure, such as 20-25 psig (138-172 kilopascals), andintroduced through liquid inlet port 12 into and around the annularliquid distribution applicator ring assembly 13. Assembly 13 includesapplicator support member 14 having grooved annular distribution ring 15in its outer edge. Multiple (e.g. four) liquid inlet tubes 16 arepositioned at preferably equal intervals around distributor 15, and aslightly larger diameter flexible distribution tube 17 is positionedaround the inner end of each inlet tube 16. The inner wall of flexibletube 17 and the outer wall of inlet tube 16 are preferably sized to forma press fit for support of tube 17. Positioned within support member 14is a ring formed of absorbent material 18 as the aforementioned firstflexible and resilient means. A preferred absorbent material is anopen-celled polyurethane foam, as for example "Omalon 9," manufacturedby the Olin Corporation (120 Long Ridge Road, Stamford, Conn. 06904).This particular foam has "Wicking Capability". In general, "WickingCapability" is the ability of an absorbent material to soak up a liquid.

From annular distributor ring 15 the liquid flows very evenly througheach inlet tube 16 because of the substantial pressure drop. Asillustrated, the four flexible inner distribution tubes 17 arepositioned within and entirely enclosed by the first means 18 at 90degree intervals around the annular ring 15, and in the same transverseplane as the first means. Accordingly, tubes 17 are essentially normalto the longitudinal movement of the inflated tubing through liquidapplicator-smoother assembly 11. The flexible inner distribution tubes17 are thus surrounded by the absorbent first means 18 so that theliquid must flow from the tubes 17 onto and around the inflate flexibletubing surface.

The Wicking Capability of the absorbent material (preferably comprisingfirst means 18) allows the liquid to be distributed around the exteriorwall of the inflated tubing. This absorbent first means 18 is alsoflexible and resilient so that it expands and contracts with the tubingwhenever the inflated tubing diameter changes. Thus it allows inflatedflexible tubing of varying diameter to remain in contact with the edge19a as the tubing passes through inner circular opening 19 of firstmeans 18.

The inner circular opening 19 is of slightly smaller diameter than thenormal diameter of the inflated flexible tubing moving longitudinallytherethrough. Preferably the diameter of the inner circular opening ofthe absorbent-type first means is between about 12% and about 20%smaller than the Normal Outside Diameter of the inflated tubing. If thisrelationship is less than about 12%, an under-inflated flexible tubingmay not remain in contact with opening edge 19a. On the other hand, ifit is more than about 20%, the inner opening 19 may be too small toallow the inflated tubing to freely pass through the opening. Therelationship between these dimensions and the amount of liquid pressurein the inlet tubes 16 determines the amount of liquid which can beapplied to the longitudinally moving tubing exterior wall.

Spaced downstream from liquid distribution applicator assembly 13 issecond flexible and resilient means 20. In some liquid coatingoperations the second means may be formed of the same material as thefirst means and preferably has Wicking Capability. However, when liquidsmoke is to be applied to the external surface of a cellulose tubing,the second means is preferably formed from flexible and resilientmaterial without Wicking Capability.

In this particular embodiment second member 20 is preferably formed ofan open-celled polyester foam. The open cellular foam member 20 is 0.5inch (1.3 cm) thick and is provided with inner circular opening 28 ofslightly smaller diameter than the outer diameter of the normal inflatedflexible tubing.

Second means 20 is positioned between spacer 21 and retaining ring 22,which is in turn secured to housing 23. The smoother assembly comprisingelements 21, 22 and 23 is joined to the outer end of rotor 24 which ismechanically connected to drive mechanism 25. The entire assembly, withthe exception of drive mechanism 25, is assembled within housing 26.

In operation, the inflated flexible tubing 27 is continuously moved inthe longitudinal direction along a straight line as for examplerepresented by its centerline axis X--X in FIG. 4, into the liquidapplicator-smoother assembly 11.

The inflated tubing 27 first moves through the inner circular opening 19of first flexible and resilient means 18 in a direction substantiallynormal to the opening diameter d--d and in rubbing contact with theopening edge 19a whose contacting surface is generally parallel with theinflated tubing exterior wall, ignoring irregularities in each surface.Simultaneously, liquid smoke flows inwardly as a multiplicity ofdiscrete streams through inlet tubes 16 and joins flexible tubes 17 fordischarge into the first means 18. The so-discharged liquid isabsorptively dispersed between the discharge regions within the entirecircumference of the absorptive material, and is distributed to edge 19afor application therefrom to the tubing wall.

As previously explained, this so-applied liquid has a tendency to flowto the underside of tubing 27 if the latter's longitudinal movement ishorizontal. This can be avoided by moving the casing still in the samestraight line X--X through rotating center opening edge 29 whosecontacting surface is generally parallel with the inflated tubingexterior wall, ignoring irregularities in each surface. The rotatingflexible and resilient second means' inner circular opening 28 is ofslightly smaller diameter than the diameter of the inflated tubingexterior wall moving longitudinally therethrough with liquid thereon. Ina preferred embodiment, the second flexible and resilient means' innercircular opening 28 is between about 4% and about 7% smaller than theNormal Outside Diameter of the inflated flexible tubing. The rotatingopening edge 29 is in rubbing contact with the liquid-coated exteriorwall and is displaced thereby, so as to simultaneously smooth the liquidcoating as a continuous film of substantially uniform thickness on thetubing exterior wall. If the aforementioned diameter relationship isless than about 4%, the inflated tubing may not remain in sufficientcontact with the second resilient means 20 to assure that the liquidwill be smoothed uniformly. On the other hand, if it exceeds about 7%,the second resilient means 20 may act as a doctoring device andundesirably scrape off liquid instead of smoothing the liquid on theinflated tubing external surface as needed to give a substantiallyuniform liquid film coating.

The rotational speed of second flexible and resilient means 20 isselected on the basis of opposing considerations. It should besufficient to aid in redistributing the liquid evenly onto the flexibletubing exterior surface. However, the rotational speed of second means20 should not be so high as to cause centrifugal spin-off of the liquidfrom the inflated tubing exterior wall. For the illustrated anddescribed embodiment, to apply a uniform liquid smoke coating to acellulose tubing, a rotational speed of 200-250 RPM has been foundsuitable.

It is to be noted that the tar-depleted, concentrated, liquid smokecomposition which is applied or "coated" on the casing surface, whetherexternally or internally, does not exist solely as a surface coating.Smoke color, odor and flavor constituents which are coated on thesurface penetrate the cellulosic structure of the casing as thecellulose absorbs the moisture of the smoke solution. Inspection of thecross-section of the casing wall discloses a color degradation acrossthe casing wall, with the smoke treated surface having a darker colorthan the surface on the opposite side of the casing wall. Accordingly,as used, herein, the term "coating" or "coated" is meant to apply to acasing wall that is not only coated with smoke constituents, but also isimpregnated with smoke constituents.

The liquid smoke compositions of the invention may also contain otheringredients which may be suitably used in treatment of a tubular foodcasing, to which the smoke constituents are applied, e.g., glycerineand/or propylene glycol, and the like, may be used as humectants orsoftening agents.

Other ingredients which are normally used in the manufacture of, or forfurther treatment of the food casings, e.g. cellulose ethers and mineraloil, may also be present in the casing if desired, and they may be usedin the same manner and amounts as if the liquid smoke composition of theinvention had not been used.

In particular, agents for improving the peelability of the casings fromfood products such as sausages, e.g. frankfurters, bolognas and thelike, may be optionally coated on the internal surface of the casingsbefore or after the external application of tar-depleted, concentrated,liquid smoke composition to the casing, and before or during shirring.If the tar-depleted liquid smoke is applied to the casing internalsurface, the peelability agent is preferably applied first. Suchpeelability enhancing agents include, but are not limited to,carboxymethyl cellulose, methyl cellulose, and other water solublecellulose ethers, the use of which is disclosed in U.S. Pat. No.3,898,348 issued Aug. 5, 1975 to Chiu, et al.; "Aquapel", a trademarkedproduct, made by Hercules, Inc., Wilmington, Del., comprising alkylketone dimers, the use of which is further disclosed in U.S. Pat. No.3,905,397 issued Sept. 16, 1975 to Chiu; and "Quilon", a trademarkedproduct, made by E. I. DuPont de Nemours Co., Wilmington, Del.,comprising fatty acid chromyl chlorides, the use of which is furtherdisclosed in U.S. Pat. No. 2,901,358 issued Aug. 25, 1959 to W. F.Underwood et al.

The peelability enhancing agent may be applied to the internal surfaceof the tubular food casings by using any one of a number of well knownmethods. Thus, for example, the peelability enhancing agent can beintroduced into the tubular casing in the form of a "slug" of liquid, ina manner similar to that disclosed, for example, in U.S. Pat. No.3,378,379 issued Apr. 16, 1968 to Shiner et al. Advancing the casingpast the liquid slug coats the inner surface thereof. Alternatively, thepeelability enhancing agent may be applied to the internal surface ofthe casing through a hollow mandrel over which the casing is advancingas, for example, a shirring machine mandrel in a manner similar to thatdescribed in U.S. Pat. No. 3,451,827, issued June 24, 1969 toBridgeford.

The method of this invention is also suitable for producing a printedcasing, e.g., a casing having an insignia, trademark, lettering, and thelike printed thereon, having smoke coloring and smoke flavoringconstituents incorporated therein. Exemplary printed casings aredisclosed in U.S. Pat. No. 3,316,189, issued Apr. 25, 1967 to Adams.

Casings prepared using the method of this invention are also suitablefor the processing of what are conventionally known in the art as "drysausages". Unlike other types of nonfibrous and fibrous casings whichare preferably easy to peel from the food product, either by the foodprocessor before sale to the customer or by the consumer, "dry sausage"casing preferably adheres to the food product during and afterprocessing. "Kymene," a trademarked product, made by Hercules, Inc.,which is a polyamide epichlorohydrin resin, the use of which is furtherdisclosed in U.S. Pat. No. 3,378,379 issued Apr. 16, 1968 to Shiner etal., may optionally be coated on the internal surface of a casingtreated with the smoke composition of the invention to improve theadhesion of the casing to food products processed therein.

The casings treated with the liquid smoke compositions of this inventioncan then be used in conventional processes for the processing ofsausages and the like, and the smoke flavor and color constituents aretransferred to the food stuff encased in the casing.

The invention will now be more clearly understood by reference to thefollowing examples which are set forth as being merely illustrative ofthe invention and which are not intended, in any manner, to belimitative thereof.

In the following examples, the phenols and carbonyl content of liquidsmoke were determined by the following procedure. All of the samples tobe evaluated were prepared by filtering them through a Whatman No. 2filter paper or equivalent, and refrigerating them as soon as possibleafter preparation to avoid possible polymerization. All samples werediluted with distilled water in two steps. In the first step, 10 ml ofthe sample was diluted to a total volume of 200 ml, and in the secondstep, 10 ml of the solution from the first step was further diluted to atotal volume of 100 ml. For the determination of the phenols, 5 ml ofthe solution from the second step was further diluted in a third stepwith distilled water to a total volume of 100 ml. For carbonyldetermination, 1 ml of the second solution was further diluted withcarbonyl-free methanol to a total volume of 10 ml.

The procedure for the determination of the amount of phenols was amodified method for detecting the amount of phenols as2,6-dimethoxyphenol based on the procedure described by I. W. Tucker in"Estimation of Phenols in Meat and Fat", JACAC, XXV, 779 (1942).

The reagents used for determination of the phenols were:

1. Boric acid-potassium chloride buffer having a pH of 8.3, made bydiluting to 1 liter with distilled water.

a. 125 ml. of 0.4 Molar boric acid solution,

b. 125 ml of 0.4 Molar potassium chloride solution, and

c. 40 ml of 0.2 Molar sodium hydroxide solution,

2. 0.6 weight percent sodium hydroxide solution,

3. Color reagent, made by dissolving 0.25 g ofN-2,6-trichloro-o-benzoquinoneamine in 30 ml of methanol and storing ina refrigerator until used, and

4. 2,6-dimethoxyphenol (DMP) standards, made by dissolving a knownamount of DMP in a known amount of distilled water to form solutions ofbetween 1 to 7 micrograms/ml. The procedure for the determination of thephenols was accomplished by following the steps below in order;

1. 5 ml of liquid smoke sample, or 5 ml DMP standard, or 5 ml ofdistilled water (for use as blank), were added to 5 ml of pH 8.3 buffer.

2. The pH was adjusted to 9.8 using 1 ml of sodium hydroxide solution.

3. Just before use, 1 ml of the color reagent was diluted to 15 ml withdistilled water and 1 ml of the diluted color reagent was added to thetest sample.

4. The color was allowed to develop for 25 minutes at room temperature.

5. The absorbance was determined at a wave length of 580 nm in a 1 cmcolorimeter tube. The spectrophotometer was a Spectronic 20, Bausch andLomb, Rochester, N.Y.

6. A standard curve was prepared from the data of the DMP standards withabsorbance as the abscissa and concentrations of the standards as theordinate. The equivalent concentrations of phenols as DMP in the liquidsmoke samples were interpolated from this curve.

7. The amount of phenols as DMP concentration in mg/ml in the liquidsmoke samples were calculated by using the equation, ##EQU3## where "DF"in the above equation is the dilution factor and "0.001" is a factor toconvert micrograms to milligrams. To calculate the mg of phenols as DMPin a gram of liquid smoke, divide the above result by the weight of 1 mlof liquid smoke.

The procedure for calculating carbonyl compounds was a modifiedLappan-Clark method for determining the equivalent amount of 2-butanonebased on the procedure described in their article "Colorimetric Methodfor Determination of Traces of Carbonyl Compounds", Anal. Chem. 23,541-542 (1959). The reagents used were:

1. Carbonyl-free methanol, prepared by adding 5 g of2,4-dinitrophenylhydrazine (DNP) to 500 ml of methanol and a few dropsof HCl, refluxing for three hours, and then distilling,

2. DNP solution, made by dissolving twice recrystallized DNP incarbonyl-free methanol to form a saturated solution. (The solution wasstored in a refrigerator and it was prepared fresh every two weeks. Itwas prewarmed before use to insure saturation.)

3. KOH solution, made by dissolving 10 g KOH in 20 ml distilled waterand diluting to 100 ml with carbonyl-free methanol, and

4. 2-butanone (methyl-ethyl-ketone) (MEK) standard solution, prepared byadding known amounts between 3 to 10 mg of MEK in 100 ml carbonyl-freemethanol (used to make standard curve).

The procedure used for determining the amount of carbonyl compounds wasas follows:

1. To 25 ml volumetric flasks containing 1 ml of DNP reagent add 1 ml ofdiluted liquid smoke solution, or 1 ml of standard MEK solution, or 1 mlof methanol (for reagent blank),

2. Add 0.05 ml of concentrated HCl to all 25 ml flasks, mix contents ofeach, and place in a water bath at 50° C. for 30 minutes,

3. Cool to room temperature and add 5 ml KOH solution to each,

4. Dilute contents of each flask to 25 ml with carbonyl-free methanol,

5. Using a Spectronic 20 spectrophotometer and 0.5×4 inch (1.27×10.2 cm)cuvettes, calibrate the spectrophotometer by reading at a wave length of480 nm against the methanol blank and setting the absorbance at 0.

6. Using data for MEK, plot absorbance versus MEK concentration forstandard curve,

7. Interpolate concentration of MEK equivalent in diluted liquid smokesolutions from this curve.

8. Calculate the carbonyl concentration as mg MEK/100 ml liquid smoke bythe following equation: ##EQU4## where "DF" is the dilution factor. Tocalculate carbonyls as mg MEK/g liquid smoke, divide the result of theabove equation by the weight (in grams) of 100 ml of the smoke beingtested.

In the examples the Color Browning Index (CBI) was determined asfollows:

(1) Prepare a phthalate buffer solution (pH 5.5) by diluting to 1000 mlwith distilled water, 500 ml of 0.1M potassium hydrogen phthalate and 76ml of 0.5M NaOH;

(2) Prepare a 2% Glycine buffer solution by dissolving 2 g of glycine in100 ml of the pH 5.5 phthalate buffer;

(3) Add 10 ml of the phthalate buffer solution to a 20×150 mm test tube;

(4) Add 10 ml of the glycine buffer solution to another 20×150 mm testtube;

(5) Add 1.0 ml of distilled water and 10 ml of glycine to serve as areagent blank;

(6) Cap the tubes with marbles and warm the tubes in a boiling waterbath for 20 minutes;

(7) Dilute the liquid smoke solution to be tested with methanol at aratio of 1 part liquid smoke to 50 parts methanol;

(8) To the tube containing the glycine buffer (reaction sample) and thetube containing the phthalate buffer only (unreacted control) add 1.0 mlof the diluted liquid smoke;

(9) Allow the color reaction to proceed at 100° C. for exactly 20minutes, after which the tubes are removed from the boiling water bathand cooled in an ice bath for 2 minutes;

(10) Using the spectrophotometer with cuvettes 0.5 in (12.7 mm) diameteror equivalent, determine the optical density of the reaction sample andthe unreacted control at a wave length of 400 nm, by reading against theglycine-water blank set at an optical density of 0.

(11) From the optical density of the reaction sample (ODR) and theoptical density of the reacted control (ODU), determine the ColorBrowning Index (CBI) from the following formula:

    CBI=[(ODR-ODU)+0.14]×dilution factor×0.65

The CBI is a measure of the quantity of potential color formingsubstances present per unit of liquid smoke.

EXAMPLE I

A tar depleted, concentrated, liquid smoke of this invention was madeusing a laboratory procedure. To about 17.8 liters of an as-is liquidsmoke (Charsol® C-12, from Red Arrow Products Company, Manitowoc, Wis),were added 1800 milliliters of methylene dichloride, and the mixture wasthoroughly mixed and allowed to settle. After the two phases separated,the tar rich solvent layer was decanted from the resultant aqueoustar-depleted liquid smoke fraction. The tar-depleted, liquid smokefraction was divided into four nearly equal portions and each portionwas placed into a shallow tray, 30.5 cm wide and 45.7 cm in length. Thefour trays with the liquid smoke solution therein were placed in aforced draft hood with a draft of air being blown across the surface ofthe solution in the trays for about 3 days. The temperature during thistime was about room temperature (about 20° C. to 30° C.). In Table A areshown the initial weights of the tar-depleted liquid smoke (initial),the weights of the final concentrated, unneutralized liquid smoke(final), and the concentration ratio for each tray.

                  TABLE A                                                         ______________________________________                                                 Initial       Final     Conc.                                        Tray No. Weight (g)    Weight (g)                                                                              Ratio                                        ______________________________________                                        1        4147.1        1057.9    3.92                                         2        4542.6        1075.6    4.22                                         3        4819.2        1196.9    4.02                                         4        4710.8        1133.0    4.16                                         ______________________________________                                    

The concentration ratio for the entire sample was 4.08

The as-is smoke (as-is), the tar-depleted liquid smoke fraction (T-DF)and the tar-depleted, concentrated liquid smoke (T-DC) of the invention,were tested and chemically analyzed. The results are summarized in TableB. Shown are the total acidity in weight percent, the concentrations ofphenols and carbonyls, and the Color Browning Index (CBI).

                  TABLE B                                                         ______________________________________                                        Smoke Total    Phenols  Carbonyls     Absorptive                              Type  Acidity  (mg/ml)  (mg/ml)  CBI  Power                                   ______________________________________                                        As-is*                                                                              11.8     13.4     134.     10.5 0.4                                     T-DF  11.7     4.1      25.5     10.3 0.2                                     T-DC  23.5     5.4      675.     34.2 0.7                                     ______________________________________                                         *Average Value for "Charsol C12                                          

The viscosity of the tar-depleted, concentrated liquid smoke (T-DC) was95 centipoise at 25° C. While this is somewhat higher than that of water(1 cp), the solution is not noticeably more viscous.

The results shown in Table B demonstrate that the total acid content ofthe tar-depleted, liquid smoke fraction does not proportionally increasewith concentration. Although the concentration ratio was about 4, theincrease in total acid content was only somewhat over a factor of 2.This previously unknown and surprising fact allows the production ofconcentrated liquid smokes that can be neutralized without anundesirably large increase in the viscosity.

Another surprising result is the relative concentrations of theflavoring and coloring constituents in the tar-depleted, concentratedliquid smoke composition, as represented by the concentration of thephenols and the carbonyls. The concentration of the phenols, which isbelieved to contribute mostly to flavor, is decreased to a value ofabout one-third of the original smoke due to the extraction of the tars.The phenols, however, did not increase significantly with theconcentration of the tar-depleted liquid smoke fraction. This iscontrary to the expectation that phenolic flavor constituents wouldbecome too concentrated in a concentrated liquid smoke composition. Aconcentration higher than about 30 mg/ml will generally result in astrong, unpalatable taste for the treated food product. However, atconcentrations below this amount, the phenols contribute to thedesirable "smoke" taste.

The concentration of the carbonyl compounds, however, significantly andunexpectedly increased with concentration of the tar-depleted liquidsmoke fraction. The concentration was more than an order of magnitude,and substantially greater than would be expected from the concentrationratio. This is very desirable since the carbonyls contribute to thecoloring ability. Therefore, this unexpected increase is very desirableand contributes significantly to the superior coloring ability of thetar-depleted, concentrated, liquid smoke compositions of the invention,as shown by the CBI and the absorptive power.

Thus, we see illustrated by this example the superior properties of thetar-depleted, concentrated, liquid smoke compositions of this invention.The unexpected, but desirable, concentrations of the phenol and carbonylconstituents are believed to be due to chemical reactions andvapor/liquid equilibrium properties of the tar-depleted liquid smokefraction that are not completely understood.

EXAMPLE II

Two samples of a concentrated, tar depleted, liquid smoke were madeessentially by the laboratory process of Example I. The concentrationratio of each was about 4:1. One sample was left unneutralized, whilethe second was partially neutralized to a pH of about 5 by the additionof sodium hydroxide flakes. For comparison, a tar-depleted liquid smokefraction, made by a solvent extraction process, was made by a procedureessentially as an Example I. Thereafter, the tar-depleted, liquid smokefraction was partially neutralized to a pH of about 5, by the additionof sodium hydroxide pellets. This tar-depleted, preneutralized liquidsmoke fraction was then concentrated by the laboratory procedure ofExample I to a concentration ratio of about 4:1. The viscosity wasmeasured using a Brookfield Viscometer Model LTV at 25° C. for eachsample. The results are summarized in Table C. Shown are the viscositiesand the pH values of the tar-depleted, concentrated, liquid smoke ofthis invention (T-DC), the tar-depleted, concentrated, partiallyneutralized liquid smoke of this invention (T-DCN), and thetar-depleted, preneutralized, concentrated liquid smoke (T-DNC).

                  TABLE C                                                         ______________________________________                                        Liquid                                                                        Smoke          pH    Viscosity (cp)                                           ______________________________________                                        T-DC*          2     95.                                                      T-DCN*         5     197.5                                                    T-DNC#         5     1185.                                                    ______________________________________                                         *Composition of this invention.                                               #Comparison composition not of this invention.                           

As shown by the data in Table C, concentration of a liquid smoke thathas been neutralized results in a composition of high viscosity.However, by practice of the invention, concentrated liquid smokecompositions can be made that have a low viscosity and can, therefore,be used easily in commercial process equipment.

EXAMPLE III

Samples of the concentrated, liquid smoke of the invention as well as anon-concentrated liquid smoke, for comparison, were prepared and theabsorptive power of each was determined. Similar samples were alsoprepared and applied to a non-fibrous gel stock casing. The absorbanceanalysis results are shown in Tables D and E; liquid smokes in Table Dand the casings in Table E. The liquid smokes were obtained by thelaboratory procedure described in Example I.

The method and apparatus used to coat the tar-depleted, concentratedliquid smoke was the same as that shown in FIG. 4 and described in theabove-cited U.S. 4,356,216.

In Table D are shown the concentration ratio and absorptive power of theliquid smoke compositions of this example. The values for absorptivepower are the average values of two measurements. In Table E are shownthe concentration ratio and absorptive index of the casings of thisexample. Liquid Smoke 1 of Table D was not concentrated and casing 1 ofTable E was made using a nonconcentrated smoke.

                  TABLE D                                                         ______________________________________                                                     Concentration                                                                             Absorptive                                           Number       Ratio       Power                                                ______________________________________                                        1            --          0.238                                                2            2:1         0.318                                                3            3:1         0.510                                                4            3.5:1       0.723                                                ______________________________________                                    

                  TABLE E                                                         ______________________________________                                                     Concentration                                                                             Absorptive                                           Number       Ratio       Index                                                ______________________________________                                        1            --          0.152                                                2            3.5:1       0.333                                                3              4:1       0.319                                                ______________________________________                                    

These results show the enhanced coloring capability of the liquid smokeand casing of the invention. Both the absorptive power and theabsorptive index are significantly higher for the tar-depleted,concentrated, liquid smoke compositions and coated casings of theinvention, as compared with non-concentrated liquid smokes and casingstreated therwith, thereby demonstrating the superior coloring ability ofcompositions and casings of this invention. The fact that theconcentrated liquid smokes having this enhanced coloring ability can bemade with a low viscosity and low phenolics, as is demonstrated inExamples II and III, is surprising.

EXAMPLE IV

Tar-depleted, concentrated, liquid smoke was made on a pilot scale usingan agitated-film evaporator for the concentration.

A tar-depleted liquid smoke was first made. To a glass-lined PfaudlerExtractor Model 13.4-12 V-35, having a capacity of 500 gal (1890 liter),was added 3035 lb (341 gal) [1377 kg (1291 liter)] of Charsol®C-12liquid smoke, followed by 516 lb (46 gal) [234 kg (174 liter)] ofmethylene dichloride. The mixture was thoroughly mixed for 1 hour, afterwhich the mixing was stopped and the phases were allowed to separate forone hour. The methylene dichloride tar-rich phase was pumped out of thebottom of the extractor, leaving 2892 lb (324 gal) [1312 kg (1226liter)] of the final tar-depleted, liquid smoke fraction.

The tar-depleted liquid smoke fraction was concentrated using aSybron/Pfaudler wiped-film evaporator having an area of 13.4 square feet(1.24 square meters) of evaporating surface and having a condenser withan internal area of 35 square feet (3.25 square meters). The evaporatorwas obtained from the Pfaudler Co., Division of Sybron Corp., Rochester,N.Y. and is described in their "Bulletin 1109, Pfaudler Wiped FilmEvaporator".

The rate of the liquid smoke as delivered to the inlet port was suchthat a concentration ratio of about 4:1 was achieved. The operatingconditions were controlled such that the liquid smoke was at no pointheated above about 50° C. The evaporator jacket was heated using"Dowtherm A"®, heat exchanger fluid (Dow Chemical, Midland, Mich.)heated electrically to 50° C. The tar-depleted liquid smoke made abovewas fed to the inlet port at an average rate of 42 pounds per hour (19kilograms per hour). A total of about 730 pounds (330 kilograms) ofconcentrated, tar-depleted, liquid smoke was produced to give aconcentration ratio of about 4:1. The evaporation was done under areduced pressure of 25 mm Hg absolute (3300 Pascals).

EXAMPLE V

Frankfurters were prepared in casings treated with tar-depleted,concentrated, liquid smoke and the coloring ability of the treatedcasings was determined.

A tar-depleted liquid smoke was prepared as in Example I, and it wasapplied to a nonfibrous gel stock casing using the method described inExample III. The casings were dried and shirred, and then stuffed andprocessed by the conventional steps of cooking, cold water showering,and chilling, but without the conventional step of smoke treatment. Theprocessing conditions were sufficient to cause the transfer of smokecolor, odor, and flavor constituents from the casing to the encasedfrankfurter. The frankfurters were then peeled and the colorimetricvalues "a" and "L" were determined.

Three meat emulsions were tested, two beef/pork emulsions, identified asEmulsions BP-1, and BP-2, and a turkey emulsion, identified as EmulsionT. BP-1 and BP-2 were made using the same formulations using differentsources of meat. In Tables F and G are shown the formulations used forthe emulsions.

In Table H are shown the colorimetric values obtained from the loadingsof liquid smoke and the emulsions shown. The colorimetric values wereobtained using a Gardner XL-23 Colorimeter with a 1 cm aperturestandardized with a white plate, all in accordance with the standardoperating procedures described in the instruction manual for the GardnerXL-23 Tristimulus Colorimeter, which is commonly used in industry forthe measurement of color.

For each meat emulsion and loading, several frankfurters were tested.Three locations on each frankfurter tested were selected formeasurement. Measurement locations were approximately 2.5 cm from theend of the frankfurter and in the middle. The frankfurters were turned180 degrees and measured in those same locations. For each emulsion acontrol using a casing that was not treated with liquid smoke was madeand tested.

"L" and "a" measurements were obtained. The "L" value measures lightnessand darkness, the higher values representing a lighter color. The "a"values measure redness, the higher the value indicating a redderproduct.

The loadings in Table H are the "effective loadings" of the liquid smokesolution or the equivalents to loadings of a nonconcentrated smoke. Forexample, a loading of 1.5 mg/cm² of a 4:1 concentrated liquid smokesolution is an effective loading of 1.5×4=6.0 mg/cm².

                  TABLE F                                                         ______________________________________                                        Beef/Pork Emulsion                                                            Emulsions BP-1 and BP-2                                                                             Weight                                                  Ingredients           (kg)                                                    ______________________________________                                        Beef Chuck            22.68                                                   Regular Pork Trimmings                                                                              22.68                                                   Water/Ice             9.07                                                    Salt                  1.13                                                    Spice                 0.45                                                    Prague Powder (Sodium Nitrite)                                                                      0.06                                                    ______________________________________                                    

                  TABLE G                                                         ______________________________________                                        Turkey Emulsion                                                               Emulsion T                                                                                          Weight                                                  Ingredients           (kg)                                                    ______________________________________                                        Mechanically Deboned Turkey                                                                         45.36                                                   Water/Ice             4.54                                                    Salt                  1.13                                                    Spice                 0.45                                                    Prague Powder (Sodium Nitrite)                                                                      0.13                                                    ______________________________________                                    

                  TABLE H                                                         ______________________________________                                        Colorimetric Data                                                                      Loading                                                              Emulsion (mg/cm.sup.2)                                                                            L      ΔL                                                                             a    Δa                               ______________________________________                                        T        0          49.5   --     14.8 --                                     T        5.87       45.1   -4.4   15.9 1.1                                    BP-1     0          50.9   --     16.2 --                                     BP-1     5.87       48.2   -2.7   16.8 0.6                                    BP-2     0          52.1   --     14.3 --                                     BP-2     5.87       48.6   -3.5   15.0 0.7                                    ______________________________________                                    

The results of the tests shown in Table H show how the tar-depleted,concentrated, liquid smoke of the invention can be used to obtain adesirably dark meat product. The meat emulsions used were relativelylight emulsions, and by practice of the invention these emulsions werecolored to an extent impractical with non-concentrated liquid smoke,using the same type of casing. Using an unconcentrated, tar-depletedliquid smoke, a loading upon a nonfibrous casing of only about 10 mg/in²(1.55 mg/cm²) is possible in one application of liquid smoke. Thus toobtain a higher loading on a nonfibrous casing, one must resort to theimpractical method of applying the liquid smoke to the casing with twoor more applications. Using the concentrated, tar-depleted, liquid smokeof the invention, higher loadings are possible with only oneapplication, allowing for greater flexibility and ease in obtaining adesired high coloring ability for use with light meat emulsions.

EXAMPLE VI

A tar-depleted, concentrated liquid smoke was made essentially as inExample I. The final pH of the tar-depleted, liquid smoke was about 2.2and the concentration ratio was about 4:1. Portions of the tar-depleted,concentrated, liquid smoke were partially neutralized with an amount ofNaOH pellets to give three samples of tar-depleted, concentrated,neutralized, liquid smoke having pH values of about 4, 5, and 7respectively. Additionally, samples of unconcentrated, tar-depletedliquid smoke were partially neutralized and then concentratedessentially as in Example I. The viscosity of the samples was measuredat about 25° C. and the results are summarized in Table I and FIG. 5. InTable I are shown the pH values and the viscosities of the liquid smokesolutions made. The viscosity was measured using a BrookfieldSynchro-Lectric Viscometer Model LTV. For Samples 1 to 5, a No. 1spindle was used, for Sample 6 a No. 3 spindle was used. For samples 1to 3, and 6, the speeds of the spindle were 30 and 60 rpm, for Sample 4,6 rpm and 12 rpm and Sample 5, 12 rpm and 30 rpm. Sample 1 wasunneutralized, Samples 2 to 4 were concentrated, then neutralized, andSamples 5 to 7 were neutralized, then concentrated.

                  TABLE I                                                         ______________________________________                                        Sample        pH     Viscosity (cp)                                           ______________________________________                                        1             2.17    20                                                      2             4.02    35                                                      3             5.00    60                                                      4             6.94   290                                                      5             4      125                                                      6             5      1190                                                     7             7      Gellation                                                ______________________________________                                    

As seen from Table I and FIG. 5, the viscosities of the samplesneutralized before concentration were dramatically higher than thosesamples made according to the invention, wherein an unneutralized liquidsmoke was concentrated. Attempts to concentrate a tar-depleted, liquidsmoke having a pH higher than about 5 was impossible due to gellation ofthe liquid smoke as it was being concentrated, whereas the tar-depleted,concentrated, neutralized liquid smoke samples made according to theinvention had viscosities sufficiently low to be commercially useful.

EXAMPLE VII

The liquid smoke composition prepared according to Example IV waspartially neutralized to a pH of 4 under conditions where thetemperature of the solution was maintained below 40° C. This liquidsmoke solution was applied on a production scale to a gel-stocknonfibrous casing at a level of about 10 milligrams per square inch(1.55 milligrams per square centimeter) according to the method andapparatus described in previously cited U.S. Pat. No. 4,356,216. Thefinal casing yielded finished frankfurters having good smoke color,which was significantly darker than the color of either the frankfurtersmade in a non-smoked control casing, or in a similarly producedunconcentrated smoke treated casing.

We claim:
 1. A method for imparting smoke color, odor, and flavor to afoodstuff comprising contacting a surface of a food casing with atar-depleted, concentrated, liquid smoke composition having a total acidcontent less than about 40 weight percent, made by contacting anaqueous, substantially unneutralized, tar-containing, liquid smokesolution and a liquid solvent at a volume ratio of about 1:1 to about65:1, respectively, under conditions to form a tar-enriched, liquidsolvent fraction and an aqueous, substantially unneutralized,tar-depleted, liquid smoke fraction, the tar-depleted, liquid smokefraction having an absorptive power of at least about 0.15 at a wavelength of 340 nm and a light transmittance of at least about 50%, thetar-containing liquid smoke solution having an absorptive power of atleast about 0.25 at a wave length of 340 nm, the liquid solvent beingnonreactive with the liquid smoke solution or reactive with the liquidsmoke solution to form a derivative liquid solvent, the liquid solventbeing immiscible in the liquid smoke solution, the liquid solvent havinga hydrogen bonding solubility parameter in the environment of the liquidsmoke solution of at least about 2.7; separating the tar-depleted,liquid smoke fraction from the tar-enriched liquid solvent fraction, andconcentrating the tar-depleted, liquid smoke fraction at a temperatureless than about 70° C. to a concentration ratio of between about 2:1 toabout 5:1 to form the tar-depleted, concentrated, liquid smokecomposition, said thus-treated food casing having an absorptive index offrom about 0.25 to about 0.9 at a wavelength of 340 nm; stuffing saidcasing with a foodstuff; and processing said casing with said foodstufftherein under conditions sufficient to transfer smoke color, smoke odor,and smoke flavor constituents from said casing to the encased foodstuff.2. A method for imparting smoke color, odor, and flavor to foodstuffcomprising contacting a surface of a food casing with a tar-depleted,concentrated, liquid smoke composition, derived from a substantiallyunneutralized, tar-depleted liquid smoke fraction having an absorptivepower of at least about 0.15 at a wavelength of 340 nm and a lighttransmittance of at least about 50%, the liquid smoke fraction havingbeen concentrated at a temperature of less than about 70 C. to aconcentration ratio of between about 2:1 and 5:1, said tar-depleted,concentrated, liquid smoke composition having a total acid content lessthan about 40 weight percent and a viscosity less than about 500centipoise at 25° C., said thus-treated food casing having an absorptiveindex of from about 0.25 to about 0.9 at a wavelength of 340 nm,stuffing said casing with foodstuff, and processing said casing withsaid foodstuff therein under conditions sufficient to transfer smokecolor, smoke odor, and smoke flavor constituents from said casing to theencased foodstuff.
 3. A method for imparting smoke color, odor, andflavor to a foodstuff comprising contacting a surface of a food casingwith a partially neutralized tar-depleted, concentrated, liquid smokecomposition derived from a substantially unneutralized tar-depletedliquid smoke fraction having an absorptive power of at least about 0.15at a wavelength of 340 nm and a light transmittance of at least about50%, the liquid smoke fraction having been concentrated at a temperatureof less than about 70° C. to a concentration ratio of between about 2:1and 5:1, said tar-depleted, concentrated, liquid smoke compositionhaving a total acid content less than about 40 weight percent and aviscosity less than about 500 centipoise at 25° C., said thus-treatedfood casing having an absorptive index of from about 0.25 to about 0.9at a wavelength of 340 nm, stuffing said casing with foodstuff, andprocessing said casing with said foodstuff therein under conditionssufficient to transfer smoke color, smoke odor, and smoke flavorconstituents from said casing to the encased foodstuff.
 4. A method forimparting smoke color, odor, and flavor to a foodstuff comprisingcontacting a surface thereof with a tar-depleted, concentrated, liquidsmoke composition having a total acid content less than about 40 weightpercent, made by contacting an aqueous, substantially unneutralized,tar-containing, liquid smoke solution and a liquid solvent at a volumeratio of about 1:1 to about 65:1, respectively, under conditions to forma tar-enriched, liquid solvent fraction and an aqueous, tar-depleted,substantially unneutralized, liquid smoke fraction, the tar-depleted,liquid smoke fraction having an absorptive power of at least about 0.15at a wave length of 340 nm and a light transmittance of at least about50%, the tar-containing liquid smoke solution having an absorptive powerof at least about 0.25 at a wave length of 340 nm, the liquid solventbeing nonreactive with the liquid smoke solution or reactive with theliquid smoke solution to form a derivative liquid solvent, the liquidsolvent being immiscible in the liquid smoke solution, the liquidsolvent having a hydrogen bonding solubility parameter in theenvironment of the liquid smoke solution of at least about 2.7;separating the tar-depleted, liquid smoke fraction from the tar-enrichedliquid solvent fraction, and concentrating the tar-depleted, liquidsmoke fraction at a temperature less than about 70° C. to aconcentration ratio of between about 2:1 to about 5:1 to form thetar-depleted, concentrated, liquid smoke composition.
 5. A method forimparting smoke color, odor, and flavor to a foodstuff comprisingcontacting a surface thereof with a tar-depleted, concentrated, liquidsmoke composition derived from a substantially unneutralized,tar-depleted liquid smoke fraction having an absorptive power of atleast about 0.15 at a wavelength of 340 nm and a light transmittance ofat least about 50%, the liquid smoke fraction having been concentratedat a temperature of less than about 70° C. to a concentration ratio ofbetween about 2:1 and 5:1, said tar-depleted, concentrated, liquid smokecomposition having a total acid content less than about 40 weightpercent and a viscosity less than about 500 centipoise at 25° C.